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Abstract:

A piston for an internal combustion engine may include a piston head and
a piston shaft. The piston shaft may have two shaft walls, one arranged
on a pressure side and the other arranged on a counter-pressure side. Two
box walls may have pin bosses and connect the shaft walls. Each of the
box walls may have a first partial wall section and a second partial wall
section. The first partial wall section may extend between the pin boss
and the shaft wall arranged on the pressure side. The second partial wall
section may extend between the pin boss and the shaft wall arranged on
the counter-pressure side. A first longitudinal centre line of the first
partial wall section is may be convergent to a second longitudinal centre
line of the second partial wall section, wherein the first and second
longitudinal centre lines--intersect each other outside the piston.

Claims:

1. A piston for an internal combustion engine comprising: a piston head
and a piston shaft adjoining thereon, the piston shaft having two shaft
walls, wherein one of the shaft walls is arranged on a pressure side and
the other of the shaft walls is arranged on a counter-pressure side, and
two box walls connecting the shaft walls, at least one pin boss disposed
in each of the box walls, each of the box walls having a first partial
wall section and a second partial wall section, the first partial wall
section extending between the pin boss and the shaft wall arranged on the
pressure side, and the second partial wall section extending between the
pin boss and the shaft wall arranged on the counter-pressure side, a
first longitudinal centre line of the first partial wall section being
convergent to a second longitudinal centre line of the second partial
wall section, wherein the first and second longitudinal centre lines
intersect each other outside the piston.

2.-13. (canceled)

14. The piston according to claim 1, wherein the shaft wall arranged on
the pressure side is shorter in a peripheral direction of the piston than
the shaft wall arranged on the counter-pressure side.

15. The piston according to claim 1, wherein each box wall has a third
partial wall section and a fourth partial wall section, each third
partial wall section extending between the pin boss and the shaft wall
arranged on the pressure side, and each fourth partial wall section
extending between the pin boss and the shaft wall arranged on the
counter-pressure side, a third longitudinal centre line of each third
partial wall section inside the piston intersects with a fourth
longitudinal centre line of each fourth partial wall section.

16. The piston according to claim 15, wherein each of the first and
second partial wall sections have a greater wall thickness than each of
the third and fourth partial wall sections.

17. The piston according to claim 15, wherein a distance between the two
box walls decreases as each third partial wall section extends inwardly
towards the shaft wall arranged at the counter pressure side and as each
fourth partial wall section extend inwardly towards the shaft wall
arranges at the pressure side.

18. The piston according to claim 15, wherein each of the fourth partial
wall sections extend away from each other in the direction of the shaft
wall arranged on the counter-pressure side.

19. The piston according to claim 15, wherein each of the respective
third and fourth partial wall sections extend towards each other in the
direction of the shaft wall arranged on the pressure side and in the
direction of the shaft wall arranged on the counter-pressure side.

20. The piston according to claim 15, wherein each third and fourth
partial wall section is convex with respect to an orthogonal of the axis
of the pin boss.

21. The piston according to claim 15, wherein each of the fourth partial
wall sections extend away from each other in the direction of the shaft
wall arranged on the counter-pressure side.

22. The piston according to claim 21, wherein each of the respective
third and fourth partial wall sections extend towards each other in the
direction of the shaft wall arranged on the pressure side and in the
direction of the shaft wall arranged on the counter-pressure side.

23. The piston according to claim 1, wherein each of the first partial
wall sections of the two box walls extend towards each other in the
direction of the shaft wall arranged on the pressure side.

24. The piston according to claim 1, wherein each of the second partial
wall sections of the two box walls extend away from each other in the
direction of the shaft wall arranged on the counter-pressure side.

25. The piston according to claim 1, wherein each of the second partial
wall sections of the two box walls extend towards each other in the
direction of the shaft wall arranged on the counter-pressure side.

26. The piston according to claim 1, wherein each of the second partial
wall sections of the two box walls extend parallel to each other.

27. The piston according to claim 1, wherein each of the first partial
wall sections of the two box walls extend away from each other in the
direction of the shaft wall arranged on the pressure side.

28. The piston for an internal combustion engine comprising: a piston
head and a piston shaft adjoining thereon, the piston shaft having two
shaft walls, wherein one of the shaft walls is arranged on a pressure
side and the other shaft wall is arranged on a counter-pressure side; two
box walls connecting the shaft walls and at least one pin boss disposed
in the box walls; each of the box walls having a first partial wall
section extending between the pin boss and the shaft wall arranged on the
pressure side and a second partial wall section extending between the pin
boss and the shaft wall arranged on the counter-pressure side, each box
wall having a third and a fourth partial wall section, the third partial
wall section extending between the pin boss and the shaft wall arranged
on the pressure side, and the fourth partial wall section extending
between the pin boss and the shaft wall arranged on the counter-pressure
side, wherein the fourth partial wall sections have at least one of a
smaller distance and a greater distance from each other at the pin boss
than at the shaft arranged on the counter-pressure side and the second
partial wall sections have at least one of a smaller distance and a
greater distance from each other at the pin boss than at the shaft
arranged on the counter-pressure side; and a first longitudinal centre
line of the first partial wall section being convergent to a second
longitudinal centre line of the second partial wall section, the two
longitudinal centre lines of the two partial wall sections intersecting
each other outside the piston.

29. The piston of claim 28, wherein the fourth partial wall sections have
a smaller distance from each other at the pin boss than at the shaft
arranged on the counter-pressure side and the second partial wall
sections have a smaller distance from each other at the pin boss than at
the shaft arranged on the counter-pressure side.

30. The piston of claim 28, wherein the fourth partial wall sections have
a greater distance from each other at the pin boss than at the shaft
arranged on the counter-pressure side and the second partial wall
sections have a smaller distance from each other at the pin boss than at
the shaft arranged on the counter-pressure side.

31. The piston of claim 28, wherein the fourth partial wall sections have
a greater distance from each other at the pin boss than at the shaft
arranged at the counter-pressure side and the second partial wall
sections have a greater distance from each other at the pin boss than at
the shaft arranged on the counter-pressure side.

32. The piston of claim 31, wherein each of the second partial wall
sections of the two box walls extend towards each other in the direction
of the shaft wall arranged on the counter-pressure side.

33. The piston of claim 31, wherein each of the first partial wall
sections of the two box walls extend away from each other in the
direction of the shaft wall arranged on the pressure side.

Description:

[0001] The present invention relates to a piston for an internal
combustion engine with a piston head and a piston shaft adjoining thereon
in accordance with the introductory clause of claim 1.

[0002] From DE 10 2009 032 379 A1 a generic piston is known for an
internal combustion engine with a piston head, a top land with a
circumferential ring part and with a piston shaft, which has two shaft
walls arranged on the pressure side and the counter-pressure side, and
two box walls connecting these shaft walls. The shaft wall arranged on
the pressure side is shorter here, viewed in the peripheral direction of
the piston, than the shaft wall arranged on the counter-pressure side. To
reduce the stressing of the piston, the box walls on the pressure side
run in a straight line and obliquely, wherein the distance of the box
walls in the region of the pin bosses is greater than in the region of
the shaft wall on the pressure side.

[0003] From DE 10 2007 020 447 A1 a further generic piston for an internal
combustion engine is known, in which the shaft wall arranged on the
pressure side is shorter in peripheral direction of the piston than the
shaft wall arranged on the counter-pressure side. Hereby, the effect is
to arise that cracks scarcely still occur in the region of the pin bosses
or respectively in the region of the support of the box walls on the
underside of the piston head.

[0004] From DE 101 45 589 B4 a further piston is known for an internal
combustion engine with a piston head and a piston shaft adjoining
thereon, wherein the piston shaft consists of bearing shaft walls and box
walls lying back, which connect the shaft walls with each other, and pin
bosses set back in the direction of a pin axis to a piston axis, which
penetrate the connecting walls. The connecting walls are constructed here
in the region of their circumferential lower edge so as to be convex to
one axis, and in the region of their upper edge beneath an annular area
so as to be concave to the axis, wherein the width of the shaft walls at
the lower edge corresponds approximately to the width of the shaft walls
beneath the annular area. Hereby, in particular, a guidance of the piston
inside the cylinder is to be improved.

[0005] A further piston is known from DE 41 09 160 C2

[0006] Generally, the trend in current engine development is towards a
CO2 reduction, which is implemented by a form of so-called
"downsizing". In order to be able to reduce the oscillating mass of
pistons in internal combustion engines, in addition pistons of
lightweight construction are being increasingly used which, moreover, can
bear higher thermo-mechanical stresses. In pistons of lightweight
construction, the main objective lies in embodying the construction so as
to be optimized with regard to stress, in order to prevent crack
formations at highly stressed sites, for example on the piston head or
the highly stressed box walls on the pressure side, and at the same time
to meet the requirements for a distinct weight reduction and thereby a
reduction of the CO2 emissions. At the same time, such pistons of
lightweight construction are to have further functional characteristics,
such as for example anti-seizing property, low shaft friction and a high
degree of quiet running.

[0007] The present invention deals with the problem of indicating for a
piston of the generic type an improved embodiment which is distinguished
in particular by a reduced weight and an increased load-bearing capacity.

[0008] This problem is solved according to the invention by the subject
matter of the independent claim 1. Advantageous embodiments are the
subject matter of the dependent claims.

[0009] The present invention is based on the general idea of aligning or
respectively arranging individual partial wall sections of box walls in
pistons for the internal combustion engine in a structurally different
manner and thereby of reducing the stressing of a piston head and of a
box wall on the counter-pressure side. The piston according to the
invention has a piston head and a piston shaft adjoining thereon directly
or indirectly via an annular area, which piston shaft has two shaft walls
arranged on the pressure side and the counter-pressure side and two box
walls connecting these shaft walls. In the box walls, in turn, pin bosses
are arranged. In the region between the pin boss and the piston head,
each box wall has two partial wall sections, the first partial wall
section of which extends between the pin boss and the shaft wall on the
pressure side, and the second partial wall section of which extends
between the pin boss and the shaft wall on the counter-pressure side. A
longitudinal centre line of the first partial wall section is arranged
here in accordance with the invention so as to be staggered with respect
to a longitudinal centre line of the second partial wall section of the
same box wall, wherein the two longitudinal centre lines of the two
partial wall sections belonging to a box wall intersect each other
outside the piston. Hereby, on the one hand, an increase in strength can
be achieved and, at the same time on the other hand the elasticity can be
retained with respect to the connection of the box wall to the associated
shaft wall. This promotes not only the loading capacity of the piston
according to the invention, but in addition important characteristics
such as for example anti-seizing property, low piston friction and a high
degree of quiet running. At the same time, this structural configuration
makes possible a comparatively low weight and hence a small oscillating
mass of the piston in operation, which has a positive effect on the
CO2 emissions of the internal combustion engine. Depending on the
individual arrangement or respectively alignment of the individual
partial wall sections of the box walls, in addition to an increase in
stability, realized for example by first partial wall sections running
towards each other in the direction of the shaft wall on the pressure
side, an improved and advantageous arrangement of an injection nozzle can
also be achieved, which can be achieved in particular by first partial
wall sections running away from each other respectively in the direction
of the shaft wall on the pressure side. Through the first partial wall
sections running away from each other, more space is available for the
positioning of the injection nozzle, whereby the latter can be arranged
more flexibly. The advantages with regard to stability and arrangement of
the injection nozzles can also be transferred here to the pressure side
by a corresponding alignment of the second partial wall sections in the
direction of the shaft wall on the counter-pressure side.

[0010] In an advantageous further development of the solution according to
the invention, each box wall has in the region beneath the pin boss, i.e.
in a region facing away from the piston head, a third and a fourth
partial wall section, of which the third partial wall section runs
between the pin boss and the shaft wall on the pressure side, and the
fourth partial wall section runs between the pin boss and the shaft wall
on the counter-pressure side. A longitudinal centre line of this third
partial wall section intersects here a longitudinal centre line of the
fourth partial wall section inside the piston, so that the third and
fourth partial wall sections are preferably arranged so as to be convex
with respect to an orthogonal to the axis of the pin boss. Hereby, for
example, also in the region beneath the pin boss, i.e. on a side of the
piston shaft facing away from the piston head, via the alignment or
respectively orientation of the individual partial wall sections of the
box walls a direct influence can be made on the stability and the weight
and the possible positioning of the injection nozzle. If, for example,
the stability is to be increased on the counter-pressure side, in this
case the respectively fourth partial wall sections of the two box walls
beneath the pin boss would have to run towards each other in the
direction of the shaft wall on the counter-pressure side. In an improved
arrangement possibility for the injection nozzle, on the other hand, the
two fourth partial wall sections of the two box walls would have to run
away from each other in the direction of the shaft wall on the
counter-pressure side. The same applies in an analogous form, of course,
for the pressure side.

[0011] Further important features and advantages of the invention will
emerge from the sub-claims, from the drawings and from the associated
description of the figures with the aid of the drawings.

[0012] It shall be understood that the features which are mentioned above
and which are to be explained further below are able to be used not only
in the respectively indicated combination, but also in other combinations
or in isolation, without departing from the scope of the present
invention.

[0013] Preferred example embodiments of the invention are illustrated in
the drawings and are explained in further detail in the following
description, wherein identical reference numbers refer to identical or
similar or functionally identical components.

[0014] Herein there are shown, diagrammatically respectively

[0015] FIG. 1 a piston according to the invention in different views and
sectional representations,

[0016] FIG. 2 a representation as in FIG. 1, but with differently aligned
partial wall sections of the individual box walls,

[0017] FIG. 3 further views and sectional representation of a further
possible embodiment of the piston according to the invention with, in
turn, differently oriented partial wall sections of the individual box
walls.

[0018] In accordance with FIGS. 1 to 3, a piston 1 according to the
invention for an internal combustion engine has a piston head 2 and a
piston shaft 4 adjoining thereon via an annular area 3. Different annular
grooves 5, for example to receive piston rings, are provided in the
annular area 3. The piston shaft 4 has two shaft walls 6 and 7 arranged
on the pressure side DS and the counter-pressure side GDS, which walls
are connected with each other via two box walls 8 and 9 (cf. in
particular the sectional representations). Pin bosses 10 or respectively
at least bores for such pin bosses 10 are arranged in the box walls 8 and
9. According to the invention, each box wall 8, 9 now has two partial
wall sections 11, 12 in the region between the pin boss 10 and the piston
head 2, of which the first partial wall section 11 runs between the pin
boss 10 and the shaft wall 6 on the pressure side, and the second partial
wall section 12 runs between the pin boss 10 and the shaft wall 7 on the
counter-pressure side. A longitudinal centre line 13 of the first partial
wall section 11 is arranged here so as to be staggered with respect to a
longitudinal centre line 14 of the second partial wall section 12,
wherein the two longitudinal centre lines 13, 14 intersect each other
outside the piston 1 in an intersection point 15. In all the pistons 1
which are shown, furthermore, the shaft wall 6 arranged on the pressure
side DS is shorter in the peripheral direction of the piston 1 than the
shaft wall 7 arranged on the counter-pressure side GDS, as can be clearly
seen in particular in the respective sectional representations B-B.

[0019] In a region beneath the pin boss 10, each box wall 8, 9 has a third
and a fourth partial wall section 16, 17, of which the third partial wall
section 16 runs between the pin boss 10 and the shaft wall 6 on the
pressure side, and the fourth partial wall section 17 runs between the
pin boss 10 and the shaft wall 7 on the counter-pressure side. A
longitudinal centre line 18 of the third partial wall section 16
intersects here a longitudinal centre line 19 of the fourth partial wall
section 17 inside the piston 1 in an intersection point 15'. The third
and fourth partial wall sections 16, 17 are arranged so as to be convex
with respect to an orthogonal to the axis 20 of the pin boss 10.
Generally, the first and second partial wall sections 11, 12 have a
greater wall thickness than the third and fourth partial wall sections
16, 17 of the respective box walls 8, 9. In addition, a distance of the
two box walls 8, 9 between the pin boss 10 and the piston head 2 is
smaller than a distance of the box walls 8, 9 beneath the pin boss 10.

[0020] The individual possible embodiments and the advantages which are
able to be achieved therewith are now to be explained more precisely
below.

[0021] In the piston 1 illustrated in FIG. 1, the respectively first
partial wall sections 11 of the two box walls 8, 9 run towards each other
in the direction of the shaft wall 6 on the pressure side (cf. sectional
representation A-A). The inclination of the two longitudinal centre axes
13, 14 of the two partial wall sections 11, 12 is comparatively small
here, so that the intersection point 15 is only drawn for the sake of
clarity, but would not have had space on the drawing without an
interruption for distance.

[0022] The running towards each other of the two first partial wall
sections 11 of the two box walls 8, 9 in the direction of the shaft wall
6 is represented by the relationship of the two reference values W>X.
Accordingly, the running away from each other by the second partial wall
sections 12 of the two box walls 8, 9 in the direction of the shaft wall
7 on the counter-pressure side is described by the relationship of the
two reference values D<C. The running away from each other by the two
second partial wall sections 12 not only makes possible a reduction to
the weight, but also at the same time a more flexible arrangement of an
injection nozzle, which is not described in further detail, wherein the
two second partial wall sections 12 could of course also be arranged
parallel to each other, wherein in this case the relationship D=C would
then apply. Through the running towards each other on the pressure side
DS by the two first partial wall sections 11 and, connected therewith,
the comparatively close arrangement of the two partial wall sections 11,
a distinct increase in the stability of the piston 1 can be achieved. The
reference values W, A, B, X, Y, Z are understood respectively to mean a
distance of the partial wall sections from each other at the boss
connection or respectively at the shaft connection.

[0023] If one views the sectional representation B-B, it can be seen that
the two third partial wall sections 16 of the two box walls 8, 9 run
towards each other in the direction of the shaft wall 6 on the pressure
side, whereby here also an increase in stability can be achieved. By
comparison, the two fourth partial wall sections 17 of the two box walls
8, 9 run away from each other in the direction of the shaft wall 7 on the
counter-pressure side, whereby an increased flexibility can be achieved
with regard to the arrangement of the injection nozzle. At the same time,
the weight can also be reduced in this area.

[0024] In the piston 1 represented in accordance with FIG. 2, the two
first partial wall sections 11 of the two box walls 8 again run towards
each other in the direction of the shaft wall 6 on the pressure side,
which is illustrated by the relationship W>X. In an analogous manner
to the sectional representation A-A of FIG. 1, the two second partial
wall sections 12 of the two box walls 8, 9 run away from each other in
the direction of the shaft wall 7 on the counter-pressure side, which is
demonstrated by the relationship D<C. Here, also, it is conceivable
that the relationship D=C applies, so that the longitudinal centre axis
14 of the second partial wall sections 12 runs orthogonally to the pin
axis 20. Through the alignment of the individual partial wall sections
11, 12 of the two box walls 8, 9, selected in the sectional
representation A-A of FIG. 2, an increase in stability can be achieved in
the region of the pressure side DS, and a reduction in weight and a
flexible arrangement of the injection nozzle can be achieved in the
region of the counter-pressure side GDS.

[0025] In the sectional representation B-B of FIG. 2, the third and fourth
partial wall sections 16, 17 of the two box walls 8, 9 are arranged so as
to be convex with respect to an orthogonal of the pin axis 20 of the pin
boss 10, which is expressed by the relationships Z>Y and A>B. In
this case, therefore, an increase in stability is achieved both on the
pressure side DS and also on the counter-pressure side GDS, because the
third partial wall sections 16 and the fourth partial wall sections 17
run towards the respectively associated shaft wall 6, 7 and are arranged
comparatively closely adjacent to each other there. An intersection point
of the individual longitudinal centre lines 18, 19 of the respective
partial wall sections 16, 17 lies inside the piston 1 here.

[0026] The piston 1 according to FIG. 3 is distinguished by two first
partial wall sections 11, which run away from each other in the direction
of the shaft wall 6 on the pressure side and thereby make possible a
weight reduction and a flexible arrangement of the injection nozzle. The
running away from each other by the two first partial wall sections 11 in
the direction of the shaft wall 6 on the pressure side is expressed by
the relationship W<X. Of course, it is also conceivable that the two
first partial wall sections 11 of the two box walls 8, 9 run parallel in
the direction of the shaft wall 6 on the pressure side, which would then
be expressed by the relationship W=X. On the counter-pressure side GDS,
on the other hand, the two second partial wall sections 12 run towards
each other in the direction of the shaft wall 7 on the counter-pressure
side, whereby in this case an increase in stability is able to be
achieved. The sectional representation B-B of the piston 1 of FIG. 3
corresponds substantially to the sectional representation B-B of FIG. 2,
wherein the two longitudinal centre axes 18, 19 again intersect each
other in an intersection point 15', which lies inside the piston 1.

[0027] However, all the embodiments have in common the fact that the
intersection point 15 of the two longitudinal centre axes 13, 14 of the
two partial wall sections 11, 12 lies outside the piston 1.

[0028] The partial wall sections 11, 12, arranged staggered with respect
to each other, of the two box walls 8, 9 therefore make possible a saving
on weight in the relationships D<C and W<X, and an increase in
stability in the relationships D>C and W>X. In addition, in the
relationships D<C and W<X an increased flexibility can be achieved
with regard to the arrangement of the injection nozzle. Of course, it is
also generally conceivable that the first and second partial wall
sections 11, 12 are arranged so as to be convex with respect to an
orthogonal to the axis 20 of the pin boss 10, wherein in this case then
with respect to the third and fourth partial wall sections 16, 17 the
relationship Z<Y and A<B would apply. This would make possible an
increase in the stabilities in the region of the shaft wall 6 on the
pressure side and of the associated first partial wall sections 11 and
the third partial wall sections 16, and an increase in stability in the
region of the shaft wall 7 on the counter-pressure side exclusively in
the region of the second partial wall sections 12, whereas the shaft wall
7 in the region of the fourth partial wall sections 17 undergoes an
increase in stability, but merely an improved and more flexible
arrangement of the injection nozzle.

[0029] For the piston 1 according to FIG. 1, it applies that: [0030] the
fourth partial wall sections 17 at the boss connection have a smaller
distance from each other than at the shaft connection A<B, [0031] the
second partial wall sections 12 at the boss connection have a smaller
distance from each other than at the shaft connection D<C, [0032] a
longitudinal centre line 13 at the height of the boss nadir of the first
partial wall section 11 is arranged staggered with respect to a
longitudinal centre line 14 of the second partial wall section 12, [0033]
the two longitudinal centre lines 13, 14 of the two partial wall sections
11, 12 intersect each other outside the piston 1.

[0034] For the piston 1 according to FIG. 2, it applies that: [0035] the
fourth partial wall sections 17 at the boss connection have a greater
distance from each other than at the shaft connection A>B, [0036] the
second partial wall sections 12 at the boss connection have a smaller
distance from each other than at the shaft connection D<C, [0037] a
longitudinal centre line 13 at the height of the boss nadir of the first
partial wall section 11 is arranged staggered with respect to a
longitudinal centre line 14 of the second partial wall section 12, [0038]
the two longitudinal centre lines 13, 14 of the two partial wall sections
11, 12 intersect each other outside the piston 1.

[0039] For the piston 1 according to FIG. 3, it applies that: [0040] the
fourth partial wall sections 17 at the boss connection have a greater
distance from each other than at the shaft connection A>B, [0041] the
second partial wall sections 12 at the boss connection have a greater
distance from each other than at the shaft connection D>C, [0042] a
longitudinal centre line 13 at the height of the boss nadir of the first
partial wall section 11 is arranged staggered with respect to a
longitudinal centre line 14 of the second partial wall section 12, [0043]
the two longitudinal centre lines 13, 14 of the two partial wall sections
11, 12 intersect each other outside the piston 1.

[0044] The boss nadir is understood here to mean the base point of the pin
boss 10, which lies beneath the zenith and the equator of the pin boss
10.